The present invention concerns mechanical couplings and, in particular, tight and rigid mechanical couplings intended to join the ends of all-purpose pipes.
There are numerous methods of tight mechanical coupling aimed at making possible the paired junction of the ends of successive lengths of pipe belonging to a same pipeline. As is standard, in such a junction of two pipe ends, it is common for at least one of those ends to remain smooth or to undergo just a simple preparatory treatment, such as, for example, cold stress, turning or the like.
Such techniques are applicable to the fabrication of tubular members and fittings (sleeves, elbows, tee-pieces, reducers, crosses, etc.) or for making various sectioning, adjusting, control or fluid moving mechanisms, like, for example, valves, caps, pumps and others. They make it possible to introduce the smooth or shaped joint of one of the lengths of pipe into the tubular mechanical joint of the other length, while the junction operation is then limited to the tightening of nuts, screws and/or bolts in order to secure a tight and rigid connection between said lengths. Thus, for example, the laying of pipe is facilitated compared to the case in which those lengths of pipe are joined by welding or by screw or flange couplings.
Most of the techniques of the prior art of tight mechanical coupling have been around for a long time and a large number of them are used primarily in the field of small-diameter pipes, that is, those in which the upper limit can be conventionally fixed at an inner diameter of approximately 40 mm. For pipes having a greater diameter, in which butt weld or flanged joints are generally preferred, those techniques have been much less widespread. When they have been used, they have been divided into three main types, each with their own disadvantages and the use of which is, in practice, limited to certain categories of pipe systems or for repairs, by reason of their costs or their conditions of use.
These three main types of coupling techniques are:
Technique 1: Coupling Using the Gland Principle
The smooth tubular joint is in this case considered the part serving as axis, and the mechanical joint Which receives it is fabricated as a gland. The xe2x80x9cpackingxe2x80x9d then often boils down to a simple O-ring seal, frequently made of elastomer. A split elastic ring is inserted between a washer, which serves to equalize the compression on the seal, and the forcing nut, so that this ring is wedged on the smooth tubular joint and the connection of the two joints is thus obtained, at the same time as the required tightness. Beyond a certain limit in the diameter of the pipe to be connected, that is, approximately 60 mm in practice, the nut is to be replaced by a flange. Some of the difficulties of a flange coupling are thus repeated in a technique which per se is not the most economical one. It follows that in the range of diameters greater than the said value, namely, approximately 60 mm, the coupling technique according to the gland principle is used when the other methods, such as butt welding of the pipe ends or welded flange connection, are ill advised or more difficult to employ or even more expensive. This situation is peculiar, that is, rather uncommon, when the pipes have a diameter greater than approximately 60 mm.
Technique 2: Joint with circular groove
Each pipe joint to be connected bears a circular groove, which can xe2x80x9ccomexe2x80x9d from casting if the joint forms part of a piece made by casting, or which can be obtained by machining or by cold stress. The two pipe ends to be joined are connected to each other by a tight collar made of elastomer, which is then covered in turn by two half-shells that fit into the aforesaid tubular grooves at the same time as they fit into each other. Finally, the half-shells are joined by bolts to secure the mechanical connection of the assembly and to keep the collar in position.
This technique is economical in the case of pipes with repetitive elements, like, for example, those of sprinkler systems. It loses a part of that advantage when the pipes are xe2x80x9cmade to order,xe2x80x9d which is often the case on building sites or industrial sites. Furthermore, it suffers from another considerable disadvantage: except in the case of sleeves or reducers, it is impossible to fabricate a fitting (for example, an elbow, tee-piece, cross, etc.) or a mechanism (for example, a valve, a pump, etc.) in a single assembly to be mounted between tubular ends. It is necessary to attach to that fitting or mechanism as many sleeves as there are ends to be connected.
Technique 3: Split sleeve coupling
The sleeve assembly functions as a single split elastic ring that is tightened by two cross screws and in which an elastomer collar is arranged, the inner diameter of which diminishes or increases depending upon whether said screws are tightened or loosened. Before tightening, a smooth tubular joint is introduced at each end of the sleeve and then the screws are tightened, which determines the tightness of the mechanical connection. It is possible to improve the latter from the standpoint of resistance to the longitudinal stresses produced by circulation of the fluid, by equipping the sleeve with two gripping parts.
The split sleeve technique improves the ease of laying pipe as well as flexibility of use, regardless of the diameter of pipe to be connected. The fabrication of sleeves is, however, relatively expensive. Furthermore, the resulting cost of laying pipe is increased even more by the fact that, as in technique 1 mentioned above, only the sleeves can exist as a complete assembly making it possible to connect two smooth joints. As for the other fittings (elbows, tee-pieces, etc.) and elements such as cocks and valves, those fittings or elements should be made with smooth tubular ends and it is necessary for as many sleeves to be added to them as there are smooth ends to be connected to the smooth joints of the pipe.
More concretely, the prior art can be illustrated by the following documents:
Patent application FR 2,694,063 describes a tight mechanical coupling using one mating flange for compression of the seal and a second mating flange for the respective attachment of the tubular joints to be assembled.
In the pre-examination publication of patent application DE 3,908,060 a pipe connection device is described with two hollow half-shells, tightened by two bolts and acting on two intermediate elastic members in order to result in attachment of the assembly. In the device thus described tightness can be achieved only if the material of the articulation part permits or if a joint filler is added, which entails, in practice, bonding of the junction.
U.S. Pat. No. 4,466,642 describes a pipe fitting system with screwing acting on a casing outside the fitting, which is split over its entire length, by means of two reinforcing bars that have the effect of generating and maintaining plastic deformations.
Patent application EP 0,756,120 describes a system for pipe coupling by straight sleeves. The straight sleeve body used is split over its entire length, is tightened from outside and activates a seal by radial compression, as well as intermediate gripping rings necessary for attachment.
A need therefore existed for tight mechanical couplings that are economical and polyvalent for connections between a smooth tubular joint and a mechanical joint belonging to another pipe end for a wide variety of areas of application.
The object of the present invention is to provide a specific method for overcoming those disadvantages and combining the advantages of the three types of techniques mentioned above.
That objective has come to be achieved, together with others which will emerge in the course of this description, thanks to a device employing a pipe fitting operation and necessitating the tightening of only one screw.
The device according to the invention comprises, in its basic structure, a mechanical joint containing a circular seal, a gland ring, an elastic ring, a back-up ring and a body, while said mechanical joint can further optionally contain a counterseal and said body can further optionally contain a closure and backing part.